1. Field of the Invention
The present invention relates to a method of manufacturing a concrete form or mold which can be used as an injection mold or the like.
2. Description of the Prior Art
Manufacture a mold or a form using concrete to reduce mold expenses such as injection molding is known. FIG. 2 shows such a conventional mold or form manufacturing method in which a master model 1 is enclosed by a frame 2 and concrete 5 is filled inside the frame 2 through an filling hole 4 provided on a top section 3 of the frame 2. After the concrete 5 hardens, the frame 2 is removed from the concrete 5 to provide a concrete form or mold. Reference numeral 2a is a small vent hole for mold venting.
FIG. 3 shows an example in which such a concrete form or mold is used as an injection mold. This injection mold is provided with a movable mold 6 and a stationary mold 7 and molding resin is filled in a cavity 8 formed by both the movable and stationary molds 6, 7 through an filling hole 7a by an injection machine. The movable mold 6 and the stationary mold 7 are the above-mentioned concrete forms or molds, wherein the movable mold 6 is provided with a mold surface 6a copied from the master model 1 to provide an external appearance surface of a molded article.
In the case of the concrete form or mold, when the concrete is filled into the frame 2, it is not possible to faithfully copy the shape of the master model 1 unless the concrete is fully filled therein. In this case, correction of the concrete form or mold is required after manufactured. This not only requires a great deal of time and labor, but also costs a great deal. It was therefore necessary to establish a method of manufacturing the concrete form or mold which makes it possible to fully fill the concrete in the frame 2.
Further, the concrete form or mold has a peculiar characteristic whereby pinholes can be easily produced on the surface thereof. Inferior outer appearance of the molded article often results from the pinholes generated on the mold surface. As shown in FIG. 3, the pinhole 9 may be formed on the surface of the mold surface 6a facing the cavity 8 parallel to the mold opening direction. If part of the molding resin 13 enters the pinhole 9 during injection molding and hardens there, there is some possibility that the movable mold 6 will not be easily opened. Accordingly, it was also necessary to decrease the generation of the pinholes.
It is therefore an object of the present invention to realize these demands or requests.
To solve the problems, in one aspect of the present invention, there is provided a method of manufacturing a concrete form or mold by providing a frame on a master model and filling concrete into the frame, which comprises the steps of filling the concrete more than the predetermined cubic volume into the frame and then, forcibly applying pressure to the concrete to the predetermined cubic volume.
A method of manufacturing a concrete form or mold according according to another aspect of the present invention includes a frame which is provided with a body section for receiving concrete of the predetermined cubic volume and a concrete receiver for receiving concrete more than the predetermined cubic volume, the method comprising the steps of causing the concrete to overflow from the body into the concrete receiver and then, forcibly applying pressure to the overflowed concrete received within the concrete receiver in the direction of the inside of the body section.
When the concrete is filled into the frame, the concrete more than the predetermined cubic volume is filled therein and then, the pressure is forcibly applied to the concrete to the predetermined cubic volume. Accordingly, the concrete under pressure can enter the detailed sections of the surface of the master model to faithfully copy the shape of the master model. This can not only reduce a great deal of time for correction of the concrete form or mold after it is manufactured, but also reduce a great deal of cost. Since the concrete can be fully filled into the frame, it is possible to prevent the concrete from being improperly filled into the frame and as a result, durability of the form or mold can also be improved.
The copied surface of the concrete form or mold is made fine and smooth and generation of the pinholes on the mold surface of the concrete form or mold can be reduced by the forcible application of pressure. Accordingly, it is not only possible to reduce inferior external appearance of the mold article resulting from the pinholes, but also to make the form or mold opening smooth during injection molding.
The body section of the frame is provided with the concrete receiver, and when the concrete is filled into the frame, the concrete is caused to overflow in the concrete receiver so that it can be filled beyond the predetermined cubic volume. Then, forcible pressure is applied to the concrete overflowed within the concrete receiver to make the final filling quantity of the concrete within the body section to be the predetermined cubic volume. It is therefore possible to efficiently perform the forcible application of pressure to the concrete.